1. Field
The described aspects relate to wireless communication networks, and more particularly, to apparatus, methods and systems for providing in-order delivery of data packets in wireless communication networks.
2. Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP LTE systems, and orthogonal frequency division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals, otherwise referred to as access terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out, multiple-in-single-out or a multiple-in-multiple-out (MIMO) system.
The term “handoff” refers to the process of transferring an ongoing call or data session from one node of the core network to another node of the core network. In wireless communication networks there may be multiple reasons why a handoff might occur. These reasons include, but are not limited to, when an access terminal moves away from the area covered by one cell and enters the area covered by another cell, the call is transferred (i.e., handed-off) to the second cell in order to avoid call termination when the access terminal moves outside the range of the first cell. Additionally, when the capacity for connecting new calls on a given cell is exhausted and an existing or new call from an access terminal, which is located in an area overlapped by another cell, is transferred to that cell in order to free-up some capacity in the first cell for other users.
The most basic form of handoff (handover) is when a call in progress is redirected from its current cell, referred to as the source, and the used channel in that cell to a new cell, referred to as a target, and a new channel. In terrestrial networks the source and the target cells may be served from two different cell sites or from one and the same cell site (in the latter case the two cells are usually referred to as two sectors on that cell site). Such a handoff, in which the source and the target are different cells, even if they are on the same cell site, is called inter-cell handoff. The purpose of inter-cell handoff is to maintain the call as the subscriber is moving out of the area covered by the source cell and entering the area of the target cell. A special case is possible, in which the source and the target are one and the same cell and only the used channel is changed during the handoff. Such a handoff, in which the cell is not changed, is called intra-cell handoff. The purpose of intra-cell handoff is to change one channel, which may be experiencing interference or fading with a new clearer or less fading channel.
Conventional wireless communication includes two types of data packets; Layer 2 (L2) and Layer 3 (L3). L3 data packets include application layer protocol data, for example, Internet Protocol (IP) data packets. L2 data packets are constructed by link-layer protocol to make the packets more suitable for communication over a wireless link. Thus, L2 data packets need to be processed again by a peer link-layer protocol to reconstruct the L3 packets. L2 data packets may be constructed by a first network entity and tunneled to a second network entity to be transmitted to the Access terminal (AT) via the second network entity. The L2 layer carries, e.g. Radio Link Protocol (RLP) data packets, and Route Protocol (RP) packets.
One problem associated with handoffs is that L2 data packets can be delivered and/or received out-of-order at the application layer. For an L2 handoff, which is a switch in the physical layer to a different access point, out-of-order packets are due to a new or different Radio Link Protocol (RLP) in the new route. In a network such as an Ultra Mobile Broadband network or the like, on the forward link, packets typically traverse the Access Gate Way (AGW) to the Data Attachment Point (DAP) to the evolved Base Station (eBS), and then they are sent wirelessly via RLP to the access terminal. When an access terminal performs an L2 handoff, RLP packets are tunneled from the source eBS to the target eBS, and sent to the access terminal. Thus, the target eBS and AT must manage two competing streams of RLP packets, the one tunneled from the source eBS, and the one generated locally by the local RLP. If the handoff is not well-managed, packets from the source eBS may be delayed or discarded causing a stall in communication or an inability to reassemble full IP packets, respectively, resulting in IP packet loss.
Another problem associated with handoffs is that L3 data packets can be delivered and/or received out-of-order at the application layer. For an L3 handoff, Internet Protocol (IP) data packets flow from the Access Gateway (AGW) to the source DAP to the target eBS on one path, and the AGW to the target DAP to the target eBS on another path. The target DAP and target eBS are often co-located or closer together, so that after handoff, packets traverse fewer network hops. Thus, in a UMB network or the like, on the forward link, when an L3 handoff is performed it causes the AGW to send packets directly to the target DAP/eBS. This path switch can cause Transmission Control Protocol (TCP) data packets to arrive out-of-order at the target eBS and, subsequently to the AT and the associated application being executed at the AT, because direct packets from the AGW to the target eBS take a shorter path than packets still in transit from the source DAP to the target eBS. At the Application Layer certain applications are adversely affected by out-of-order delivery of packets. For example, an application implementing TCP may be negatively impacted because out-of-order packet delivery may cause the TCP receiver to generate duplicate ACKnowledgement (ACK) messages, and cause TCP to react by reducing its congestion window.
Therefore a need exists to develop a scheme to prevent out-of-order delivery of data packets during hand-off. The desired methods, apparatus, systems and the like should increase the overall performance of AT-based applications that are adversely affected by out-of-order delivery of data packets. Additionally, the desired scheme should address Forward Link Serving eBS network and/or DAP handoffs that occur in networks such as UMB, as well as, Reverse Link Serving eBS and/or DAP handoffs.